There is widespread use of electric motors to control the actuation or movement of parts or components within various systems. Such systems include, for example, manufacturing systems, Heating, Ventilation, and Air Conditioning (HVAC) systems, as well as a host of other systems. For example, HVAC systems typically provide heating, cooling, ventilation and/or air handling within buildings or structures. In many cases, such HVAC systems incorporate the use of electric motors to achieve the desired air handling, flow control, and/or other functions of the HVAC system. For example, electric motors may be used to drive fans, blowers, actuators, pumps, valves, mixers, and the like.
A drive control assembly is often used to control the drive current that is provided to the electric motors. In some cases, Variable Frequency Drives (VFDs) are included in the drive control assembly to control the speed of the electric motor. The use of VFDs can often significantly increase the efficiency of a system, such as an HVAC system, by not requiring that the motor (e.g. fan motors) to be driven at full speed all the time. The VFD may drive the motor at an appropriate speed, depending on the current conditions and/or needs. In some cases, the VFDs can include a control module having control electronics and/or software, and in some cases a user interface, to allow the user to control the operation of the VFD, and thus the motor.
VFDs can fail in the field for any number of reasons. When a VFD fails, the corresponding motor(s) can stop or otherwise not be controlled properly, which can have a significant impact on the operation of the overall system. For example, if a VFD controlling a main fan of an HVAC system fails, the main fan may stop operating and the heated, cooled and/or ventilation air may not be delivered to the building as expected. To help combat this, many VFDs are coupled to or include a bypass function. The bypass function, when activated, provides power to the motor so that the motor can continue to operate, often at full speed, even after the VFD fails. In some cases, an operator must detect the failure of the VFD, and then manually activate the bypass function via a switch or push a button. In other cases, a control module for the VFD may automatically detect the failure in the VFD, and automatically activate the bypass function.
In many cases, the bypass function requires the presence of the VFD in order to provide proper bypass power to the motor. A problem arises when the VFD must be removed, such as for maintenance and/or replacement. During such times, the bypass function may need to be removed or deactivated, which causes the corresponding motor(s) to also be deactivated. This may be particularly detrimental in those systems where continuous operation of the motor(s) is desired or required. Therefore, it would be desirable to provide a bypass function that can remain fully functional when the VFD module is removed, replaced and/or otherwise not operational.